1. Field of the Invention
Embodiments of the invention are directed to the field of bicycle wheel rims and, more particularly, to a lighter, stronger and otherwise improved rim for tires with or without tubes.
2. Description of Related Art
The rim is the outer, usually metal, hoop of a bicycle wheel. The spokes of a bicycle wheel extend between a central hub of the wheel and the rim. An inflatable tube and/or tire are positioned around the exterior of the rim and air is introduced through a valve mechanism to inflate the tube and/or tire on the rim as a functional part of a bicycle.
A prior art rim including a mounted, inflated tire is shown in cross section in FIG. 1 to illustrate conventional rim construction. The rim 100 has a base portion 101, which holds the distal portion of a spoke assembly 102. The base portion extends upward in the form of a Y to a point 103. A mounting surface 104 of the rim has a generally concave profile and extends between, and connects to, opposing points 103. Sidewalls 105 extend outwards from points 103 and terminate in bead lock region 106. Tire 110 has tire bead regions 112. In an uninflated state, the tire bead regions 112 loosely rest on rim surface 104 in the region between sidewalls 105. Upon inflation, the bead portions ride up the surface 104 until they sealingly engage sidewalls 105. Due to the construction of the tire bead 112, the bead lock regions 106 help to stabilize the engagement of the tire with the rim. Many variations of rim designs are known to those skilled in the art. However, the great majority of rims will have the basic portions illustrated in FIG. 1.
The dimensions of various portions of a bicycle rim can significantly influence rim function. For example, weight is a significant consideration in a racing or touring rim. In addition to material considerations, rim parameters such as the inside distance between the rim sidewalls will largely determine useable tire size, the ability to use an inner tube within the tire, rim strength, the effect of forces on the rim during various maneuvers such as turning, braking, etc., and others. The shape of the surface 104 may significantly influence the ease of tube/tire mounting and tube/tire inflation. The height, shape and thickness of the rim sidewalls will contribute to overall rim weight, strength, tire stability, air leakage, and other considerations appreciated by those skilled in the art.
Several issues can be identified with respect to conventional rim construction and dimensions. Rim sidewalls typically have a height dimension, shown as H in FIG. 1, between about 0.225 inch to ≧0.265 inch for a conventional bicycle rim. As the dimension H increases, so does the mechanical leverage of the tire on the rim. The greater leverage resulting from a higher sidewall further increases the forces acting in the region of point 103 of the rim shown in FIG. 1, thus requiring additional support at points 103 in the form of more material and increased rim weight. A higher sidewall dimension, H, promotes greater flexing of the rim and may result in cracking or stress fracture of the rim material. In addition, as rim sidewall height, H, increases, available tire inflation volume decreases while inflation pressure increases. Moreover, less tire surface is available resulting in decreased traction and other disadvantages. Another consequence of high sidewalls and various bead lock sizes and shapes is the well known “pinch flat” or “snake bite” that may be caused when the tube or tire gets pinched between the rim and a hard, sharp object such as a rock, curb stone or the edge of a pothole, for example. An under-inflated tire also contributes to a pinch flat occurrence. A too soft, or too narrow (for the rim) tire more easily lets the tire bottom out when striking an obstruction resulting in the pinch holes from the bead locks or distal portion of the sidewall.
Several issues to be considered with respect to rim surface 104 as shown in FIG. 1 include rim strength, the ability to uniformly position the tire bead region on the rim prior to inflation and the ease of tire inflation, particularly with a manual pump, the interchangeable use of tubes and/or tubeless tires, and others recognized in the art. In light of the known shortcomings of conventional bicycle rim designs, such as those set forth above and others known to those skilled in the art, the inventor has recognized a need for an improved rim that addresses these disadvantages and additionally results in a lighter, stronger, more versatile, better performing and cost effective rim for the rider.